This invention relates to semi trailer dump bodies and, more particularly, to apparatus for dumping the contents of the body.
A semi trailer dumping vehicle is a very versatile vehicle for transporting a large variety of different particulate material. Vehicles of this kind include a semi trailer dumping body having a chassis that is adapted to be supported at the front by a tractor and at the rear by wheels attached to the chassis. The dumping body typically is in the form of a box with a closed bottom, side walls and a front wall and an open top. A tailgate is mounted across the rear of the body to retain the contents of the body when the tailgate is closed. The box is pivotally mounted at the rear end of the chassis so that it may be raised into a dumping position by one or more hydraulically operated cylinders pivotally attached between the front end of the chassis and the front end of the box. During dumping, it is important that the contents slide smoothly and evenly out of the box through the unloading opening and past the tailgate onto the ground or into a waiting receptacle.
Different materials slide out at different angles depending upon the shape and texture of the particulate, the weight distribution and the condition of the floor of the dump body.
If the contents of the box is dry, homogeneous and properly distributed throughout a smooth, dry dumping body, dumping can be easily and smoothly accomplished. However, moisture distributed throughout the particulate material or on the surface of the dumping body may cause the particles to stick together and to stick to the insides of the dumping body. Even if the materials is dry when it is placed into the dumping body, it can become wet while it is being transported or stored in the dumping body. After a period of use, the inside of the body often becomes dented and rough so that it will tend to inhibit the easy slideout of the commodity.
Dumping wet or frozen materials from a rough dump body can be very difficult. The particles can tend to stick together past its natural angle and then release all at once and cascade toward the unloading opening. This tends to destabilize the raised body. If parts of the payload are frozen or otherwise stuck together, the load can get hung up on the tailgate. When this happens, it can be a serious problem to free the load. It may be difficult for an operator to climb up on the raised body and loosen the load with a shovel or even to stand on the ground next to the body and try to loosen the load from below. Operators sometimes try to lower and then raise the dump body quickly to jar the load loose. Operators have been known to attempt to drive the semi trailer away from the dumping spot with the dumping body raised in the hope that quickly acceleraing and then quickly stopping will jar the load loose.
It is also possible for one side of the load to slide before the other side. This can cause the raised dumping vehicle and the tractor to roll over, thus spilling the contents and damaging both the semi trailer dump body and tractor.
Even if destabilizing uneven breakaway does not occur, positions of the contents may stick to the insides of the dump body if it has not been properly loosened prior to dumping. Such practices as accelerating the vehicle and stopping it quickly with the dump body raised to cause the tailgate to bang against the back of the body or quickly reciprocating the cylinder hoist are usually not satisfactory ways to loosen the retained material. Manually removing the undumped contents is time consuming and thus expensive.
To alleviate this problem of the load sticking to the insides of the dump body or of the load sticking together, vibrators have been placed on the bottom of the truck body to vibrate the contents loose. Electrically driven vibrators have been used in the past which may be actuated by a switch located on the dashboard of a truck cab. See, for example, devices disclosed in U.S. Pat. Nos. 3,438,677, and 3,747,980. Other solutions have been provided for this problem by using an hydraulic vibrator mounted on the bottom of the dumping body and operated by the hydraulic fluid which drives the hoist to raise the dumping body. These devices have also been manually actuated by a control knob located on the dashboard of the cab. See, for example, U.S. Pat. No. 3,343,876. Although these devices provide adequate means for shaking a load loose, they are manually actuated and hence depend, for their proper operation, upon the skill of the operator. If the vibrator is turned on too soon before the dumping body reaches the normal dumping angle of the contents, the load will be compacted by the vibration and dumping will be made more difficult. If the vibrator is turned on after the dumping body reaches the normal dumping angle it can cause a sticking load to release too quickly and cascade out of the dumping body. This can destabilize the dumping body.
It can be undesirable to have the vibrator remain on too long after the contents have begun to slide out. It is important that the contents begin to slide out at the proper angle and that it be allowed to slide out naturally at its own pace. Vibrating the load too heavily while it is sliding, can tend to accelerate the sliding and also, perhaps, destabilize the raised vehicle.